[mythtv-users] wintv-pvr-usb2 audio clipping [solved]
Rich.West at wesmo.com
Tue Apr 24 02:01:07 UTC 2012
I'm just tossing this out there in the event someone else bumps in to this.
IMHO, it's a bit of a "needle in a haystack" kind of solution.
If there is more of a "right" way to do this, I'm all ears. :)
I replaced a PCI PVR-150 (still works, just need to free up a PCI slot) with
a WinTV-PVR-USB2. This is a straight-up replacement (pull card, move cables
over to USB device, adjust mythtv accordingly). Should be simple, one would
I get video fine, but the problem is the audio. It's as if the audio is all
of the way up and now clipping.
Google searches were plentiful (15 tabs up at the moment), which confirm
"For all hardware device types, there is a problem with distortion in the
audio when the volume is set too high. The pvrusb2 driver starts with the
volume set to the max, so you get the distortion....The workaround is easy:
lower the volume. Empirical testing here (on both types of devices) suggests
that right now 58000 is a good value for maximum gain distortion free
audio." along with another reference in the to the right value being 62000.
I scratched my head wondering just how to do that. None of the posts said how.
I found a hint here: http://www.isely.net/pvrusb2/usage.html
Down the page, under "sysfs Interface," there is a reference to ctl_volume
buried in the page. It looked promising.
So.. dig through the filesystem: /sys/class/pvrusb2/sn-xxxxxxx/ctl_volume
(where xxxxxxx is the serial number of your device). Look at the directly.
The only writable file is "cur_val" as you can't adjust the maximum here.
THAT file, the "cur_val" file, is you want to adjust.
I personally found that the following sounded better than 58000 (nearly no
clipping). I also dropped the line below in rc.local
echo 56000 > /sys/class/pvrusb2/sn-xxxxxxx/ctl_volume/cur_val
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